The invention relates to a process and apparatus for the production of metal pipes according to the preamble of claim 1 and claim 3.
1. Field of the Invention
To achieve a faultless weld seam it is of decisive importance that, on the one hand, the edges of the band to be welded are free of oil and oxide and, on the other hand, the edges of the band are guided clean and during the welding process lie exactly flush and at the same height relative to each other. For this purpose the band edges of the de-oiled metal band are trimmed immediately before the forming of the slotted pipe. Moreover, attention must be given to the deformation of the metal band into the slotted pipe.
2.Discussion of the Related Art
For metal bands of steel and copper, forming tools of steel have proven themselves which consist of pairs of forming rollers or forming cylinders. Therewith the metal band is gradually deformed between the forming rollers or forming cylinders into a slotted pipe.
For bands of metals which incline toward cold spots such as, for example aluminum, aluminum alloys, stainless steel, niobium, titanium, i.e., forming tools of plastic are used. However, their disadvantage lies in a low tool life. The use of forming tools of steel has the disadvantage that cold spots arise at the forming rollers or forming cylinders which build up more and more and change the geometry of the forming tool, which ultimately leads to an incomplete forming of the pipe and thus to a poor weld seam. These cold spots appear more at those points at which a strong deformation of the metal band is done. In the xe2x80x9cUniwemaxe2x80x9d process described, this is the first forming stage in which a radius of curvature is imparted to the areas of the edges of the bands which is present in the finished slotted pipe.
For the solution of this problem it is known from DE-U-94 03 594 that on the surface of the lower forming roller or forming cylinder turned away from the metal band, at least in the first forming stage where the deformation is greatest, a brush device engages which keeps the surface of the forming roller or forming cylinder blank.
The disadvantage of this known apparatus is to be seen in the fact that the surface of the forming rollers or forming cylinders is stressed additionally by the engagement of the brush device and not only the cold spot particles are removed. Thereby additional wear of the forming rollers or forming cylinders occurs.
Also the,brushes themselves wear and have to be exchanged, which leads to an interruption of production. Moreover, the amount of contaminants is very high, whereby the welding process is also disturbed. A quite decisive disadvantage is that an aluminum dust explosion can result with the use of aluminum bands.
If the welded pipe has to be reduced in its diameter, the same problem of cold spots also occurs in this tool since pains are taken to perform the reduction in one operational step.
This objective is realized by the features covered in claims 1 and 3.
The essential advantage of the invention is to be seen in the fact that due to the extremely high hardness of the surface of the forming cylinders or forming rollers the amount of friction between the band and the forming rollers or forming cylinders is clearly reduced. The achievable hardness is around five times higher than the hardness of traditional titanium nitride layers. A friction value of clearly under 0.1 is achieved.
Additional advantageous developments of the invention are covered in the subordinate claims.
The invention will be explained in more detail with the aid of the exemplary embodiments represented schematically in FIGS. 1 to 3.